CHERENKOV TELESCOPE ARRAY FOR INTENSITY INTERFEROMETRY Dainis - PowerPoint PPT Presentation

Intensity Interferometry workshop – Salt Lake City, January 2009 OPTIMIZING THE CHERENKOV TELESCOPE ARRAY FOR INTENSITY INTERFEROMETRY Dainis Dravins Lund Observatory, Sweden www.astro.lu.se/~dainis

CTA, Cherenkov Telescope Array

PRIORITIES IN EUROPEAN ASTRONOMY 2010-2020 ASTRONET Infrastructure Roadmap http://www.astronet-eu.org/ For the section on High-Energy Astrophysics, Astroparticle Physics and Gravitational Waves, highest-priority near-term ( − 2015) project is CTA; in overall list is 2 nd highest priority among medium-scale ground-based projects (following the European Solar Telescope). ESFPRI , European Strategy Forum on Research Infrastructures ftp://ftp.cordis.europa.eu/pub/esfri/docs/esfri_roadmap_update_2008.pdf Eight prioritized projects within Physical Sciences and Engineering, include CTA ASPERA network on astroparticle physics http://www.aspera-eu.org/ The priority project for VHE gamma astrophysics is the Cherenkov Telescope Array, CTA.

Cherenkov Telescope Array www.cta-observatory.org The CTA Design Study is to optimize the planned observatory Primary targets of are to constrain design and technology options; Optimize the cost/performance ratio; Define how CTA is to be constructed and operated; Build and test prototype telescope(s)

CTA CONSORTIUM DESIGN STUDY Approximately four years, 2008-2011 11 work packages PHYS Astrophysics and astroparticle physics MC Optimization of array layout, performance studies and analysis algorithms [MonteCarlo] SITE Site evaluation and site infrastructure MIR Design of telescope optics and mirror TEL Design of telescope structure, drive and control systems FPI Focal Plane Instrumentation ELEC Readout electronics and trigger ATAC Atmospheric monitoring, associated science and instrument calibration OBS Observatory operation and access DATA Data handling, processing, management and data access QA Risk assessment and quality assurance

PHYSICS WORK PACKAGE Work Package Coordinator: Diego F. Torres ICREA & Institut de Ciencies de l'Espai (IEEC-CSIC), Barcelona, Spain Physics WP topics & Task Leaders Dark matter / Fundamental physics — Jan Conrad Extragalactic background light / Cosmology — Daniel Mazin AGNs — Helene Sol, Catherine Boisson, Andreas Zech Cosmic rays / Clusters / Starbursts — Olaf Reimer Microquasars / Binaries — Josep M. Paredes Cosmic rays / SNRs / Molecular clouds — Stefano Gabici Pulsar-wind nebulae — Okkie de Jager Pulsars / Globular clusters — Bronek Rudak Galactic center — Stefan Funk Multi-wavelength / Transients / GRBs — Sera Markoff Timing — Dimitri Emmanoulopoulos Surveys / Sub-arrays — Guillaume Dubus Extended / Diffuse Sources — Sabrina Casanova Intensity Interferometry — Dainis Dravins Direct-Cherenkov light / CR composition — Rolf Bühler

Cherenkov Telescope Array CTA General meetings May 4-5, 2006, Berlin, Germany March 1-2, 2007, Paris, France January 24-25, 2008, Barcelona, Spain November 3-5, 2008, Padua, Italy May 11-13, 2009, Cracow, Poland

CTA desiderata Isochronous telescope design ? Parabolic or Schmidt better than Davies-Cotton for ∆ t < few ns

Cherenkov telescopes are usually Davies–Cotton or parabolic In a Davies–Cotton layout, all reflector facets have same focal length f, arranged on a sphere of radius f. In a parabolic layout, mirrors are arranged on a paraboloid, and the focal length of the (usually spherical) mirror facets varies with the distance from the optical axis. Both have significant aberrations off the optical axis, the parabolic slightly worse than Davies–Cotton. Time dispersion introduced by the reflector should not exceed the intrinsic spread of the Cherenkov wavefront of a few ns. Parabolic reflectors are isochronal – apart from minute effects caused by individual mirror facets being spherical rather than parabolic. Davies–Cotton layout causes a spread of photon arrival times at the camera; a plane incident wavefront results in photons spread over ∆ t ≈ 5 ns, with an rms width ≈ 1.4 ns. The optical system of the H.E.S.S. imaging atmospheric Cherenkov telescopes. Part I: Layout and components of the system K.Bernlöhr, O.Carrol, R.Cornils, S.Elfahem P.Espigat, S.Gillessen, G.Heinzelmann, G.Hermann, W.Hofmann, D.Horns. I.Jung, R.Kankanyan, A.Katona, B.Khelifi, H.Krawczynski, M.Panter, M.Punch, S.Rayner, G.Rowell, M.Tluczykont, R.van Staa Astropart.Phys. 20 , 111 (2003)

DAVIES-COTTON SPHERICAL REFLECTOR DESIGN The Davies–Cotton configuration forms a focal surface at the center of curvature of the optical support, 7.3 m from the mirror surface. A Davies–Cotton layout gives smaller aberrations off the optical axis compared to a parabolic design. A disadvantage is that the structure is not isochronous.: Rays striking mirrors at different distances from the optic-axis have different transit times to the focal plane. For the 10 m Whipple telescope the spread of transit times is 6.5 ns. The Whipple Observatory 10 m Gamma-Ray Telescope, 1997–2006 J. Kildea et al. , Astropart.Phys. 28, 182 (2007)

Parabolic reflector of MAGIC, Roque de los Muchachos, La Palma

MAGIC has isochronous parabolic reflectors with an intrinsic time spread of 400 ps, sufficient to resolve the time structure of the cosmic showers

INTRINSIC TIME SPREAD IN 20 m ∅ CHERENKOV TELESCOPES Top: Spherical (Davies–Cotton) A spherical reflector substantially widens the photon pulse. At detecting 10 GeV γ -showers, the pulse width on the spherical telescope's focal plane may reach 15– 20 ns instead of the inherent 5–8 ns. Angles of incidence = 2 ° Bottom: Parabolic Performance of a 20 m diameter Cherenkov imaging telescope A.Akhperjanian & V.Sahakian Astropart.Phys. 21 , 149 (2004)

INTRINSIC TIME SPREAD IN 20 m ∅ CHERENKOV TELESCOPES Top: Spherical (Davies–Cotton) Dish arrival time and camera arrival times of photoelectrons initiated by the photons from 10 GeV γ -showers. The observation height is 5 km a.s.l., and the showers impact distances are: 50 m (solid), 100 m (dashed), 150 m (dotted) and 200 m (dash-dotted). Bottom: Parabolic Performance of a 20 m diameter Cherenkov imaging telescope A.Akhperjanian & V.Sahakian Astropart.Phys. 21 , 149 (2004)

IACT Schmidt telescope Diameter 7.0 m F-ratio 0.8 Focal length 5.6 m Field of View 15 ° Resolution (RMS) < 1 ′ Non-isochronicity ≤ 0.03 ns The mirror and the focal plane have their centre of curvature at the centre of the corrector plate. The Schmidt corrector is shown with the aspheric shape magnified by a factor of 20. Both the nominal corrector and a Fresnel version is shown . R. Mirzoyan, M.I. Andersen: A 15 deg Wide Field of View Imaging Air Cherenkov Telescope Astropart.Phys. (2009) = astro-ph 0806.0297

DIGITAL PHOTON CORRELATORS @ Lund Observatory 2008/09: 700 MHz clock rate (1.4 ns time resolution) 200 MHz maximum photon count rates per channel (pulse-pair resolution 5 ns) Photon pulses at TTL voltages High-speed correlators may be limited by telescope non-isochronicity

CTA desiderata Sharper PSF gives less background Sky brightness: (a) Dark sky; m V ≈ 21.5 mag / arcsec 2 (b) Full Moon; m V ≈ 18 mag / arcsec 2 ⇒ m V ≈ 9.4 (a) and 5.9 (b) for 5 arcmin ∅ ⇒ m V ≈ 12.9 (a) and 9.4 (b) for 1 arcmin ∅ R.H.Garstang: Night-sky brightness at observatories and sites, Publ.Astron.Soc.Pacific 101 , 306 (1989)

SKY BACKGROUND COUNT RATES Expected count rates in HEGRA CT1 (4.2 m ∅ , FoV 15 arcmin) and MAGIC I (17 m ∅ , FoV 6 arcmin) ”Background” = Crab nebula background + Light Of the Night Sky during dark-sky conditions Determination of the night sky background around the Crab pulsar using its optical pulsation E.Oña-Wilhelmi, J.Cortina, O.C.de Jager, V.Fonseca Astropart.Phys. 22 , 95 (2004)

? ? ? Intensity interferometry “should” be possible to carry out in full moonlight when Cherenkov observations are not feasible

CTA desiderata Detectors for huge photon fluxes? Photon counting @ 100 MHz – 10 GHz? Silicon detector arrays?

CTA desiderata Handling high data rates ? Can photon time-tagging to 1 ns-100 ps be preserved until a computing location?

CTA desiderata Detectors – only central pixel(s) ? or should one have separate detectors?

7-pixel camera on the lid of the H.E.S.S. Cherenkov camera A 7-pixel camera was custom-built and mounted on the lid of the Cherenkov camera of a H.E.S.S. telescope using a plane secondary mirror to put it into focus. Its central pixel was used to continuously record the light curve of the target, while a ring of six ‘outer’ pixels was used both to monitor the sky background level and as a veto system to reject background events occurring in the atmosphere Capability of Cherenkov Telescopes to Observe Ultra-fast Optical Flares C.Deil, W.Domainko, G.Hermann, A.-C.Clapson, A.Förster, C.van Eldik, W.Hofmann Astropart.Phys. , in press (2009) = astro-ph 0812.3966